The Collaborative International Dictionary of English v.0.48:

Association \As*so`ci*a"tion\ (?; 277), n. [Cf. F. association,
   LL. associatio, fr. L. associare.]
   1. The act of associating, or state of being associated;
      union; connection, whether of persons of things. "Some . .
      . bond of association." --Hooker.
      [1913 Webster]

            Self-denial is a kind of holy association with God.
                                                  --Boyle.
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   2. Mental connection, or that which is mentally linked or
      associated with a thing.
      [1913 Webster]

            Words . . . must owe their powers association.
                                                  --Johnson.
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            Why should . . . the holiest words, with all their
            venerable associations, be profaned?  --Coleridge.
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   3. Union of persons in a company or society for some
      particular purpose; as, the American Association for the
      Advancement of Science; a benevolent association.
      Specifically, as among the Congregationalists, a society,
      consisting of a number of ministers, generally the pastors
      of neighboring churches, united for promoting the
      interests of religion and the harmony of the churches.
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   Association of ideas (Physiol.), the combination or
      connection of states of mind or their objects with one
      another, as the result of which one is said to be revived
      or represented by means of the other. The relations
      according to which they are thus connected or revived are
      called the law of association. Prominent among them are
      reckoned the relations of time and place, and of cause and
      effect. --Porter.
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WordNet (r) 3.0 (2006):

association
    n 1: a formal organization of people or groups of people; "he
         joined the Modern Language Association"
    2: the act of consorting with or joining with others; "you
       cannot be convicted of criminal guilt by association"
    3: the state of being connected together as in memory or
       imagination; "his association of his father with being beaten
       was too strong to break" [ant: disassociation]
    4: the process of bringing ideas or events together in memory or
       imagination; "conditioning is a form of learning by
       association" [syn: association, connection, connexion]
    5: a social or business relationship; "a valuable financial
       affiliation"; "he was sorry he had to sever his ties with
       other members of the team"; "many close associations with
       England" [syn: affiliation, association, tie, tie-up]
    6: a relation resulting from interaction or dependence; "flints
       were found in association with the prehistoric remains of the
       bear"; "the host is not always injured by association with a
       parasite"
    7: (chemistry) any process of combination (especially in
       solution) that depends on relatively weak chemical bonding
    8: (ecology) a group of organisms (plants and animals) that live
       together in a certain geographical region and constitute a
       community with a few dominant species

Moby Thesaurus II by Grady Ward, 1.0:

230 Moby Thesaurus words for "association":
   Anschluss, British Cabinet, Sanhedrin, US Cabinet, accompaniment,
   accord, accordance, addition, adjunct, advisory body, affairs,
   affiliation, affinity, agglomeration, aggregation, agreement,
   alignment, alliance, amalgamation, approximation, assemblage,
   assembly, assimilation, association by contiguity,
   association of ideas, bench, blend, blending, board,
   body of advisers, bond, bonding, borough council, brain trust,
   cabal, cabinet, cahoots, camaraderie, camarilla, cartel,
   centralization, chain of thought, chamber, city council,
   clang association, closeness, co-working, coaction, coadunation,
   coalescence, coalition, cochairmanship, coincidence, collaboration,
   colleagueship, collectivity, collegialism, collegiality, collusion,
   combination, combine, combined effort, combo, common council,
   community, companionship, company, complicity, composition,
   comradeship, concert, concerted action, concomitance, concordance,
   concourse, concurrence, condominium, confederacy, confederation,
   conference, confluence, confraternity, congeries, conglomeration,
   congress, conjugation, conjunction, connectedness, connection,
   consilience, consociation, consolidation, consortium, consortship,
   conspiracy, consultative assembly, contiguity, contrariety,
   contribution, controlled association, cooperation, cooperative,
   copartnership, copartnery, correspondence, cotenancy, council,
   council fire, council of ministers, council of state,
   council of war, county council, court, current of thought,
   dealings, deduction, deliberative assembly, diet, directory,
   disjunction, divan, ecumenism, embodiment, encompassment,
   engagement, enosis, federalization, federation, fellowship,
   filiation, flow of thought, fraternalism, fraternity,
   fraternization, free association, freemasonry, friendship, fusion,
   group, guild, having a part, homology, hookup, identification,
   inclusion, incorporation, inmost thoughts, integration,
   intercourse, intimacy, involvement, joining, joint chairmanship,
   joint control, joint ownership, joint tenancy, junction, junta,
   kitchen cabinet, league, legislature, liaison, link, linkage,
   linking, marriage, meld, melding, membership, mental linking,
   merger, mutual attraction, nearness, negative transference,
   organization, package, package deal, pairing, parasitism,
   parish council, partaking, participation, partnership,
   positive transference, privy council, propinquity, proximity,
   rapport, relatedness, relation, relations, relationship,
   saprophytism, secret thoughts, sharing, similarity, simultaneity,
   social circle, social class, society, sodality, solidification,
   sorority, soviet, staff, stream of consciousness, suffrage,
   symbiosis, sympathy, synchronism, syncretism, syndicate,
   syndication, syneresis, synergy, synesthesia, synod, synthesis,
   thoughts, tie, tie-in, tie-up, train of thought, transference,
   tribunal, unification, union, united action, voting, wedding